Diamond drill bits

ABSTRACT

Diamond drill bits for drilling oil, gas, water, mining, and similar, bore holes in formations, in which cube diamonds are set in the drilling face of a bit with the diamonds arranged in generally radial rows and with the leading or cutting faces of the diamonds also arranged generally radially to enhance cutting of certain formations, such as relatively soft or evaporite formations. The leading faces of the rows of diamonds form the trailing sides of fluid waterways or channels through which drilling fluid flows. In some forms of bits, conventional generally round rows of diamonds are used in conjunction with the cube diamonds to limit the depth of penetration of the cube diamonds into the formation.

United States Patent [1 1 Rowley et al.

[ 11' 3,709,308 1 Jan. 9, 1973 [54] DIAMOND DRILL BITS [75] inventors: David S. Rowley; Charles E. Ward,

both of Salt Lake City, Utah [73] Assignee: Christensen Diamond Products Company, Salt Lake City, Utah [22] Filed: Dec. 2, 1970 [21] Appl. No.: 94,399

[52] US. Cl. ..l75l329 [51] Int. Cl. ..E2lb 9/36 [58] Field of Search ..l75/329, 330, 410, 327

[56] References Cited UNITED STATES PATENTS 2,818,233 12/1957 Williams ..175/330 1,923,488 8/1933 Howard et al ..175/4l0 2,894,726 7/1959 Weaver et a1 ....l75/410 X 3,106,973 10/1963 Christensen ....l75/330 X 2,371,489 3/1945 Williams ..175/329 2,371,490 3/1945 Williams ..l75/329 3,027,952 4/1962 Brooks ..175/329 3,058,535 10/1962 Williams 175/330 Primary Examiner-David H. Brown I AttorneyBernard Kriegel and Kendrick, Subkow &

Kriegel [57] ABSTRACT Diamond drill bits for drilling oil, gas, water, mining, and similar, bore holes in formations, in which cube diamonds are set in the drilling face of a bit with the diamonds arranged in generally radial rows and with the leading or cutting faces of the diamonds also arranged generally radially to enhance cutting of certain formations, such as relatively soft or evaporite formations. The leading faces of the rows of diamonds form the trailing sides of fluid waterways or channels through which drilling fluid flows. In some forms of bits, conventional generally round rows of diamonds are used in conjunction with the cube diamonds to limit the depth of penetration of the cube diamonds into the formation.

22 Claims, 8 Drawing Figures DIAMOND DRILL BITS The present invention relates to rotary drill bits, and

more particularly to diamond bits used in the drilling or coring of oil, gas, water, mining, and similar, bore holes.

Rotary drilling bits embodying generally round diamonds do not penetrate adequately in the softer, sticky formations, since the diamonds tend to merely displace and deform the formation, rather than cut and remove it. In addition, with round diamonds set in the drilling face of the bit, fluid waterways or channels through which the drilling fluid is pumped are slightly removed from the cutting portions of the diamonds, which necessarily displaces the path of the high velocity flushing fluid flowing through the waterways from the formation being penetrated by the diamonds, resulting in a substantial reduction in the assistance of the high velocity flushing fluid in removing the formation.

In the drilling of evaporite formations, which are relatively elastic, instead of the formation being cut by round diamonds, or by the points of diamonds of polyhedron shape, the formation tends to deflect sub stantially under the drilling weight or load imposed on the diamonds, the cutting action of the round or pointed diamonds being reduced considerably.

By virtue of the present invention, the above difficulties encountered in drilling softer, sticky formations and evaporite formations with round diamonds or the point portions of diamonds are overcome. Diamond drill bits are used in which cubic diamonds are set in the drilling face or faces of the bit in such manner that their flat cutting faces are presented to the formation to effect its removal in the nature of a drag bit. More specifically, the leading faces of the diamonds and their lower edges are disposed in generally radial planes extending from the bit axis. The diamonds are capable of penetrating into the formation to a much greater extent than round diamonds, and do not merely displace and deform the formation, which can return elastically to its initial position after the diamond moves away from it.

The flushing action of the drilling fluid flowing through the drill bit and through its waterways, and over its ribs or lands defined by the waterways, is considerably improved since the cubic diamonds, or diamonds of polyhedron shape, are set in the bit in such manner that their leading faces form the trailing sides of the waterways that extend generally from the center or inner portion of the bit to its gauge portion, the drilling fluid flushing directly upon and flowing along such leading faces to maintain them in a clean and cool state.

By virtue of the invention, rotary diamond drill bits can be provided in which the extent of penetration of the cubic or polyhedron diamonds is controlled and limited by the inclusion of round diamonds set in the bit face. These round diamonds limit the amount of torque required to rotate the bit and, therefore, enable the torque required for transmission through the drill string to the bit to be retained at a safe value, thereby avoiding twist-offs and other types of drill string failures.

By virtue of the use of the cubic diamonds, or polyhedron diamonds of similar shape, set in the drilling face or faces of the bit in accordance with the invention, the depth of penetration of the diamonds, when compared to drill bits with round diamonds, is greater, to more effectively drill the softer and evaporative types of formations. The setting of cubic and similar diamonds in generally radial planes results in the presentation of a much larger drilling surface for action on the formation than is available when round diamonds are used, so that fewer cubic or polyhedron diamonds are required in the bit.

Diamond bits made in accordance with the present invention drill formations at a faster rate; they drill a greater footage of the bore hole; and, therefore, effect substantial reductions in drilling costs. Moreover, drill bits with cubic or similar diamonds produce larger cuttings, which are conveyed by the flushing fluid to the top of the well bore, enabling the geologist to identify the cuttings more readily.

This invention possesses many other advantages, and

has other purposes which may be made more clearly apparent from a consideration of several forms in which it may be embodied. Such forms are shown in the drawings accompanying and forming part of the present specification. These forms will now be described in detail for the purpose of illustrating the general principles of the invention; but it is to be understood that such detailed description is not to be taken in a limiting sense.

Referring to the drawings:

FIG. 1 is a combined longitudinal section and side elevational view of a drill bit embodying one specific form of the invention;

FIG. 2 is an enlarged bottom plan view taken along the line 2-2 on FIG. 1;

FIG. 3 is an enlarged sectional view taken along the line 33 on FIG. 2, illustrating the drilling action of the drill bit diamonds on the formation;

FIG. 4 is a bottom plan view of another specific embodiment of the invention;

FIG. 5 is a bottom plan view of yet a further embodiment of the invention;

FIG. 6 is an enlarged section taken along the line 6 6 on FIG. 5, illustrating the cutting actions of the diamonds in the formation;

FIG. 7 is a bottom plan view of still another form of the invention; and

FIG. 8 is an enlarged section taken along the line 8- 8 on FIG. 7, illustrating the cutting action of the diamonds of the bit in the formation.

The diamond drill bit A illustrated in Flg. 1 is capable of operating upon the bottom of a bore hole, and to flush the cuttings upwardly around the drill bit and the string of drill pipe B to which it is secured, which extends to the top of the hole and through which'drilling weight and torque is transmitted to the bit. The drill bit includes a main body or shank 10 having an upper threaded pin 11 for threadedly attaching the bit to the lower threaded box 12 of the string of drill pipe. Drilling fluid is circulated or pumped down through the drill pipe B, flowing into a central or main passage 13 in the body of the tool, from where it flows through a plurality of circumferentially spaced longitudinally extending ports or openings 14 against the bottom of the bore hole, and also through distributing channels or waterways 15 that extend laterally across the cutting surface or face 16 of the bit toward its outer portion, and the side wall of the bore hole produced by the bit.

In general, the body of the bit includes a matrix portion 17 of a known type, in which diamonds 18 are secured. As disclosed, the bit is of the type to drill the entire cross-sectional area of the bore hole. It is to be understood, however, that the invention is also applicable to other types of bits, such as core bits, in which the central portion of the bottom of the hole is not cut, so as to produce the desired central formation core. As shown, the central portion 19 of the bit is generally conical in shape, with the sides of the cone tapering in an upward and inward direction. Such conical portion merges into a lowermost bottom contacting portion 20, which, in turn, merges into an upwardly divergent coni cal face 21 that terminates at the reaming face 22 of the bit.

In the specific form of the invention illustrated in FIGS. 1 and 2, the drilling portions of the bit are divided into a plurality of diamond set ribs or lands 23 extending from the inner portion of the bit to its outer reaming face. These ribs or lands are generally radially arranged and are actually formed and spaced from each other by lateral generally radial waterways or channels that extend from the central portion of the bit, communicating with the ports or openings 14 from which they receive drilling fluid. The fluid flows in a lateral outward direction from each port, opening or passage 14, through the waterways l5 and into vertical waterways or grooves 24 in the reaming face of the bit. Some of the waterways 15 in the drilling face of the bit also extend into circumferentially spaced junk slots 25 through which cuttings can pass upwardly, discharging into the annular space between the bit body and wall of the bore hole above the matrix 17, for continued upward flow through the annulus between the drill pipe string B and wall of the bore hole.

The inner portions of the lands or ribs 23 terminate short of the axis of the drill bit, except for one of the lands which has an inner portion 23a extending to the axis, and preferably across the axis 26, to insure the cutting of the bore hole to the bit axis, so as to prevent the production of a core which might tend to retard penetration of the bit into the bottom of the hole. Suitable diamonds 27 are disposed in the inner portion 23a of such rib for action upon the bottom of the hole, these diamonds being of any desired configuration. Diamonds 27 of generally round shape are specifically illustrated in the drawings.

Circumferentially spaced rows 28 of diamonds 18 are set in the end drilling face of the bit, these diamonds being of polyhedron form. Preferably, cube diamonds 18 are used, each row of diamonds being set in a radial rib 23 at the trailing side 15a of a waterway 15, and with leading faces 18a of the diamonds and their lower edges 18b arranged generally radially of the bit axis 27, with such leading faces forming the trailing side of the waterway in conjunction with the intervening matrix material between the diamonds in each row. As disclosed most clearly in FIG. 3, the cube diamonds 18 are arranged at the trailing side of each waterway l5 and are set in the matrix 17 preferably with a negative rake, such that the leading face 18a of each diamond makes an acute angle to the formation F against which the diamond bears. As an example, the negative rake can be about 22, each diamond 18 having a forward tilt in the direction of rotation.

As illustrated specifically in FIG. 2, each row 28 of cube diamonds 18, the diamonds in each row being radially spaced from each other, is mounted in its generally radial rib 23 at the trailing side of an adjoining waterway, the row of diamonds extending from the inner portion to the outer portion of the rib. Each rib that extends outwardly to the reaming face 22 of the bit has the cube diamonds 18 extending from a longitudinal passage or port 14 to the reaming face, the vertical ribs 30 defined between the vertical waterways 24 having diamonds 31 of any suitable configuration, such as a round configuration, set in the reaming face for insuring the drilling of the bore hole to the desired diameter.

In the drilling of the bore hole, drilling weight is imposed through the drill pipe string B on the drill bit A while the drill p'ipe string and bit are rotated at the desired speed, flushing liquid being pumped down through the drill pipe string and flowing through the central bit passage 13 and its ports 14 to the bottom of the hole, from where it passes laterally through the waterways 15 toward the periphery of the bit. The cube diamonds penetrate into the formation and effecting its cutting, the drilling fluid carrying the cuttings through the waterways 15 toward the periphery of the bit, from where they pass upwardly along the bit and into the annular space above the matrix 17. The leading or cutting faces 18a and edges 18b of the diamonds produce the cuttings at the waterways, so that the flushing fluid passing throughthe waterways 15 at a high velocity are capable of directly removing the cuttings and sweeping them through the waterways toward the outer portion of the bit. Such flushing fluid actsdirectly upon the leading faces 18a of the diamond cutting elements and cleans them thoroughly of cuttings, as well as cooling the diamonds and adjoining vmatrix and maintaining them in a cool state.

Since the leading faces 18a of the diamonds are disposed generally radially of the bit, they penetrate and cut the formation in the same manner as a drag bit. Accordingly, a greater penetration is achieved in relatively soft, sticky formations, and in evaporative types of formations, to insure the formation of cuttings, the cube diamonds overcoming the elasticity of such formation materials; that is to say, the cube diamonds cut the softer or evaporative types of formations, rather than merely displacing or deforming them, as occurs in drill bits embodying round diamonds in their drilling faces. Because of the drag bit-like action of thecube diamonds 18- on the formation, larger cuttings are produced which are flushed to the top of the bore hole. The cubic diamonds present a much larger drillingsurface 18a to the formation than round diamonds, which enables fewer diamonds to be used and the bore hole drilled at a faster rate. The diamond bit embodying the cube diamonds 18 is capable of drilling a greater footage of the same formation when compared with bits embodying round diamonds.

in drill bits of larger diameter, as illustrated in FIG. 4, the outer portion of the drilling face may be provided with branching waterways 15b to form additional ribs or lands 23b in which rows 28a of the polyhedron or cube diamonds 18 can be set, in the same manner as the other rows 28 of diamonds. These diamonds 18 are set in the ribs23b at the trailing side of the supplementary waterways that communicate with the other waterways and also with vertical waterways provided in the reaming face 22, the diamonds also preferably being set in the bit face with a negative rake.

In the specific modification of drill bit illustrated in FIG. 4, the drilling action is the same as in the specific arrangement of lands, waterways and cube set diamonds illustrated in FIG. 2, except that more diamonds are available for penetration into the outer portion of the bottom of the bore hole, for effective production and removal of the formation cuttings, and to insure a long effective cutting life of the drill bit in the bore hole.

In certain types of formations, the provision of a drill bit containing substantially all cube diamonds 18 could result in excessive penetration of the diamonds in the formation, requiring the transmission of a comparatively large torque through the drill pipe string B for the purpose of rotating the drill bit at the preferred speed. As illustrated in FIGS. 5 and 6, the extent or depth of penetration of the cubic diamonds 18 is controlled and limited by the inclusion of round diamonds 40 set in the bit face. As specifically illustrated, alternate ribs 23 have cube diamonds 18 set therein which combine with the matrix material to define the trailing faces of adjacent waterways 15. The ribs 23c therebetween have generally round diamonds 40 set therein at the trailing sides of the adjacent waterways 150. The cube diamonds 18 in each row 28 are spaced radially from each other, which is also true of the round diamonds 40 in each of its rows. However, the cube diamonds in one row are in staggered relation with respect to the cube diamonds 18 of another row, such that the cube diamonds in all rows 28 collectivelycut upon the entire area of the bottom of the bore hole. Similarly, the round diamonds 40 in each row 28d are radially spaced from each other and are in staggered relation with respect to the round diamonds in another row, such that the several rows 28d of diamonds 4 0 collectively cover substantially the entire area of the bottom of the bore hole upon rotation of the drill bit.

In general, the drill bit illustrated in FIGS. 5 and 6 operates in the same manner as the drill bits illustrated in FIGS. l-4, except that the round diamonds 40 are incapable of penetrating into the formation to the same extent as the cube diamonds 18. As a result, a limit is placed upon the amount of torque required to rotate the bit with the appropriate drilling weight imposed thereon, so that twist-offs and other failures of the drill pipe string B are avoided.

The appropriate setting and retention of the round diamonds 40 in the matrix 17 of the drill bit necessitates the cutting portion 40a of each round diamond, that extends outwardly from the matrix 17, to be displaced away from the side of the waterway 150, which is particularly evident from FIG. 6. This is to be compared to the leading face 18a of the cube diamond 18 which provides the actual trailing side of the waterway l5, enabling the flushing liquid to act directly upon the diamond 18 for the purpose of removing any cuttings that tend to adhere thereto and to flush the cuttings not only from the leading faces of the diamonds but from the bottom of the hole. This direct action of the drilling fluid upon the bottom of the hole also assists the cube diamonds in producing the cuttings, since the high velocity fluid is acting directly upon the bottom F of the hole where the cutting action by the cube diamonds is occurring.

In the embodiment of invention illustrated in FIGS. 7 and 8, essentially the same combination of cube diamonds 18 and round diamonds 40 is disclosed as presented in FIGS. 5 and 6, the bit operating in the same manner. HOwever, additional flushing fluid is caused to pass along each row 28d of round diamonds 40 by providing waterways 15e, 15f immediately adjacent thereto and on each side of each row. Thus, the drilling fluid will flow through leading and trailing waterways 15e, 15f on opposite sides of each row 28d of round diamonds to cool and clean such diamonds of cuttings and to flush the cuttings toward the perimeter of the bit.

In all forms of diamond drill bits illustrated, the cube diamond l8 and also the round diamond 40 can be set in various manners. Thus, the cube diamonds 18 in each row can be set closely adjacent to each other, or spaced to any desired extent from one another, the rows of diamonds being staggered with respect to one another. As an example, FIG. 2 illustrates a closer, fairly heavy setting of the cube diamonds 18; whereas, FIG. 5 illustrates a widely spaced, or light setting, of the cube diamonds in each row, the same being true of the diamonds in each row 28d of round diamonds 40. Moreover, the size of the diamonds used can be varied to suit various drilling conditions.

We claim:

1. In a rotary bit: a body having a cutting face for drilling a hole; circumferentially spaced generally radial rows of polyhedron diamond cutting elements in said face, the cutting elements in each row having exposed leading substantially flat faces and lower cutting edges both disposed in a generally radial plane extending from the rotational axis of the bit.

2. In a rotary bit as defined in claim 1; said cutting elements being of cube form.

3. In a rotary bit as defined in claim 1; the substantially flat face of said cutting elements being disposed in said cutting face with a negative rake.

4. In a rotary bit as defined in claim 1; said cutting elements being diamonds of cube form; the substantially flat faces of said cutting elements being disposed in said cutting face with a negative rake.

5. In a rotary bit: a body having a cutting face for drilling a hole; circumferentially spaced generally radial rows of polyhedron cutting elements in said face, the cutting elements in each row having leading faces and lower cutting edges disposed in a generally radial plane extending from the rotational axis of the bit; and circumferentially spaced generally radial rows of generally round cutting elements in said cutting face interposed between said rows of polyhedron cutting elements.

6. In a rotary bit as defined in claim 5; said polyhedron cutting elements being diamonds of cube form; said generally round cutting elements being diamonds.

7. In a rotary bit as defined in claim 5; said polyhedron cutting elements being diamonds of cube form; said generally round cutting elements being diamonds; said diamonds of cube form being disposed in said cutting face with a negative rake.

8. In a rotary bit adapted to be lowered in a hole on a tubular drill string: a body having a cutting face for drilling a hole and passage means for receiving fluid from the drill string; said face having generally radial waterways communicating with said passage means and extending to the outer portion of the face and providing a plurality of lands therebetween extending laterally from an inner portion of the face to the outer portion of the face; circumferentially spaced generally radial rows of polyhedron cutting elements in a plurality of said lands adjacent to at least some of said waterways, the cutting elements in each row having exposed leading substantially flat faces and lower cutting edges both disposed in a generally radial plane extending from the rotational axis of the body, said exposed leading faces in each row forming at least a portion of the trailing side of an adjacent waterway.

9. In a rotary bit as defined in claim 8; said cutting elements being of cube form.

10. In a rotary bit as defined in claim 8; the substantially flat face of said cutting elements being disposed in said cutting face with a negative rake.

11. In a rotary bit as defined in claim 8; said cutting elements being diamonds.

12. In a rotary bit as defined in claim 8; said cutting elements being diamonds of cube form.

13. In a rotary bit as defined in claim 8; said cutting elements being diamonds of cube form; the substantially flat faces of said cutting elements being disposed in said cutting face with a negative rake.

14. In a rotary bit adapted to be lowered in a hole on a tubular drill string: a body having a cutting face for drilling a hole and passage means for receiving fluid from the drill string; said face having generally radial waterways communicating with said passage means and extending to the outer portion of the face and providing a plurality of lands therebetween extending laterally from an inner portion of the face to the outer portion of the face; circumferentially spaced generally radial rows of polyhedron cutting elements in a plurality of said lands adjacent to at least some of said waterways, the cutting elements in each row having leading faces and lower cutting edges disposed in a generally radial plane extending from the rotational axis of the body, said leading faces in each row forming at least a portion of the trailing side of an adjacent waterway; and circumferentially spaced generally radial rows of generally round cutting elements in said cutting face interposed between said rows of polyhedron cutting elements.

15. In a rotary bit as defined in claim 14; said polyhedron cutting elements being diamonds of cube form; said generally round cutting elements being diamonds.

16. In a rotary bit as defined in claim 14; said polyhedron cutting elements being diamonds of cube form; said generally round cutting elements being diamonds; said diamonds of cube form being disposed in said cutting face with a negative rake.

17. In a rotary bit adapted to be lowered in a hole on a tubular drill string: a body having a cutting face for extending to the outer portion of the face and providing a plurality of lands therebetween extending laterally from an inner portion of the face to the outer portion of the face; circumferentially spaced generally radial rows of polyhedron cutting elements in a plurality of said lands adjacent to at least some of said waterways, the cutting elements in each row having leading faces and lower cutting edges disposed in a generally radial plane extending from the rotational axis of the body, said leading faces in each row forming at least a portion of the trailing side of an adjacent waterway; and circumferentially spaced generally radial rows of generally round cutting elements in a plurality of said lands-adjacent some of said waterways and interposed between saidrows of polyhedron cutting elements.

18. In a rotary bit as defined in claim 17; said polyhedron cutting elements being diamonds of cube form; said generally round cutting elements being diamonds.

19. In a rotary bit as defined in claim 17; said polyhedron cutting elements being diamonds of cube form; said generally round cutting elements being diamonds; said diamonds of cube form being disposed in said cutting face with a negative rake.

20. In a rotary bit adapted to be lowered in a hole on a tubular drill string: a body having a cutting face for drilling a hole and passage means for receiving fluid from the drill string; said face having generally radial waterways communicating with said passage means and extending to the outer portion of the face and providing a plurality of lands therebetween extending laterally from an inner portion of the face to the outer portion of the face; circumferentially spaced generally radial rows of polyhedron cutting elements in a plurality of said lands adjacent to at least some of said waterways, the cutting elements in each row having leading faces and lower cutting edges disposed in a generally radial plane extending from the rotational axis of thebody, said leading faces in each row forming at least a portion of the trailing side of an adjacent waterway; circumferentially spaced generally radial rows of generally round cutting elements in a plurality of said lands adjacent to the trailing side of some of said waterways and interposed between said rows of polyhedron cutting elements; said cutting face having generally radial waterways adjacent the trailing side of said rows of generally round cutting elements.

21. In a rotary bit as defined in claim 20; said polyhedron cutting elements being diamonds of cube form; said generally round cutting elements being diamonds.

22. In a rotary bit as defined in claim 20; said polyhedron cutting elements being diamonds of cube form; said generally round cutting elements being diamonds; said diamonds of cube form being disposed in said cutting face with a negative rake. 

1. In a rotary bit: a body having a cutting face for drilling a hole; circumferentially spaced generally radial rows of polyhedron diamond cutting elements in said face, the cutting elements in each row having exposed leading substantially flat faces and lower cutting edges both disposed in a generally radial plane extending from the rotational axis of the bit.
 2. In a rotary bit as defined in claim 1; said cutting elements being of cube form.
 3. In a rotary bit as defined in claim 1; the substantially flat face of said cutting elements being disposed in said cutting face with a negative rake.
 4. In a rotary bit as defined in claim 1; said cutting elements being diamonds of cube form; the substantially flat faces of said cutting elements being disposed in said cutting face with a negative rake.
 5. In a rotary bit: a body having a cutting face for drilling a hole; circumferentially spaced generally radial rows of polyhedron cutting elements in said face, the cutting elements in each row having leading faces and lower cutting edges disposed in a generally radial plane extending from the rotational axis of the bit; and circumferentially spaced generally radial rows of generally round cutting elements in said cutting face interposed between said rows of polyhedron cutting elements.
 6. In a rotary bit as defined in claim 5; said polyhedron cutting elements being diamonds of cube form; said generally round cutting elements being diamonds.
 7. In a rotary bit as defined in claim 5; said polyhedron cutting elements being diamonds of cube form; said generally round cutting elements being diamonds; said diamonds of cube form being disposed in said cutting face with a negative rake.
 8. In a rotary bit adapted to be lowered in a hole on a tubular drill string: a body having a cutting face for drilling a hole and passage means for receiving fluid from the drill string; said face having generally radial waterways communicating with said passage means and extending to the outer portion of the face and providing a plurality of lands therebetween extending laterally from an inner portion of the face to the outer portion of the face; circumferentially spaced generally radial rows of polyhedron cutting elements in a plurality of said lands adjacent to at least some of said waterways, the cutting elements in each row having exposed leading substantially flat faces and lower cutting edges both disposed in a generally radial plane extending from the rotational axis of the body, said exposed leading faces in each row forming at least a portion of the trailing side of an adjacent waterway.
 9. In a rotary bit as defined in claim 8; said cutting elements being of cube form.
 10. In a rotary bit as defined in claim 8; the substantially flat face of said cutting elements being disposed in said cutting face with a negative rake.
 11. In a rotary bit as defined in claim 8; said cutting elements being diamonds.
 12. In a rotary bit as defined in claim 8; said cutting elements being diamonds of cube form.
 13. In a rotary bit as defined in claim 8; said cutting elements being diamonds of cube form; the substantially flat faces of said cutting elements being disposed in said cutting face with a negative rake.
 14. In a rotary bit adapted to be lowered in a hole on a tubular drill string: a body having a cutting face for drilling a hole and passage means for receiving fluid from the drill string; said face having generally radial waterways communicating with said passage means and extending to the outer portion of the face and providing a plurality of lands therebetween extending laterally from an inner portion of the face to the outer portion of the face; circumferentially spaced generally radial rows of polyhedron cutting elements in a plurality of said lands adjacent to at least some of said waterways, the cutting elements in each row having leading faces and lower cutting edges disposed in a generally radial plane extending from the rotational axis of the body, said leading faces in each row formiNg at least a portion of the trailing side of an adjacent waterway; and circumferentially spaced generally radial rows of generally round cutting elements in said cutting face interposed between said rows of polyhedron cutting elements.
 15. In a rotary bit as defined in claim 14; said polyhedron cutting elements being diamonds of cube form; said generally round cutting elements being diamonds.
 16. In a rotary bit as defined in claim 14; said polyhedron cutting elements being diamonds of cube form; said generally round cutting elements being diamonds; said diamonds of cube form being disposed in said cutting face with a negative rake.
 17. In a rotary bit adapted to be lowered in a hole on a tubular drill string: a body having a cutting face for drilling a hole and passage means for receiving fluid from the drill string; said face having generally radial waterways communicating with said passage means and extending to the outer portion of the face and providing a plurality of lands therebetween extending laterally from an inner portion of the face to the outer portion of the face; circumferentially spaced generally radial rows of polyhedron cutting elements in a plurality of said lands adjacent to at least some of said waterways, the cutting elements in each row having leading faces and lower cutting edges disposed in a generally radial plane extending from the rotational axis of the body, said leading faces in each row forming at least a portion of the trailing side of an adjacent waterway; and circumferentially spaced generally radial rows of generally round cutting elements in a plurality of said lands adjacent some of said waterways and interposed between said rows of polyhedron cutting elements.
 18. In a rotary bit as defined in claim 17; said polyhedron cutting elements being diamonds of cube form; said generally round cutting elements being diamonds.
 19. In a rotary bit as defined in claim 17; said polyhedron cutting elements being diamonds of cube form; said generally round cutting elements being diamonds; said diamonds of cube form being disposed in said cutting face with a negative rake.
 20. In a rotary bit adapted to be lowered in a hole on a tubular drill string: a body having a cutting face for drilling a hole and passage means for receiving fluid from the drill string; said face having generally radial waterways communicating with said passage means and extending to the outer portion of the face and providing a plurality of lands therebetween extending laterally from an inner portion of the face to the outer portion of the face; circumferentially spaced generally radial rows of polyhedron cutting elements in a plurality of said lands adjacent to at least some of said waterways, the cutting elements in each row having leading faces and lower cutting edges disposed in a generally radial plane extending from the rotational axis of the body, said leading faces in each row forming at least a portion of the trailing side of an adjacent waterway; circumferentially spaced generally radial rows of generally round cutting elements in a plurality of said lands adjacent to the trailing side of some of said waterways and interposed between said rows of polyhedron cutting elements; said cutting face having generally radial waterways adjacent the trailing side of said rows of generally round cutting elements.
 21. In a rotary bit as defined in claim 20; said polyhedron cutting elements being diamonds of cube form; said generally round cutting elements being diamonds.
 22. In a rotary bit as defined in claim 20; said polyhedron cutting elements being diamonds of cube form; said generally round cutting elements being diamonds; said diamonds of cube form being disposed in said cutting face with a negative rake. 